The purpose of the proposed studies is to examine the interrelationships among amino acid transport systems in mouse oocytes, ova and preimplantation conceptuses and intra-and extracellular amino acid concentrations. The first and fourth aims are to complete identification of the transport systems present at each stage of development and to determine the transport systems present at each stage of development and to determine the location of systems in different cell types and membrane in blastocysts. The transport systems in granulosa cells will also be characterized in aim 4, and this data and that for oocytes will aid in determining how the latter cells are nourished during oogenesis. The second aim is to determine if the transport systems are subject to trans-inhibition or trans-stimulation (exchange) by determining if uptake or exodus of amino acids via each system is inhibited or stimulated, respectively, by substrateds of the system on the opposite side of the plasma membrane. Based on these results, mixtures of animo acids will be formulated either to maintain the amino avid levels in conceptuses at the intracellular concentrations of these substances normally found in situ or to raise or lower the intracellular concentrations of one or more amino acids. It will be determined in the third aim whether differences in the intracellular concentrations of amino acids, as produced in aim 2, are associated with differences in the abilities of preimplantation conceptuses to develop normally in vitro. It will also be determined if amino acids can affect the "optimum" osmolarity at which preimplantation mouse conceptuses develop in vitro, since amino acids can be osmoregualtors and the "optimum" osmolarity of standard media is below the osmolarity of secretions of the reproductive tract. Comparison of data from aims 1-4 to similar data for other species should provide insight into how early conceptuses of different species undergo similar morphological changes in widely different environments. Oocytes and early conceptuses o different species appear to express some of the same novel amino acid transport system activities at different stages of development. Such changes during evolution in the chronology of phenotypic expression are terms heterochrony, and elucidation of the mechanism controlling expression of these transport systems could help determine a mechanism of heterochrony. These studies are also important because it should be possible to enhance or inhibit fertility relatively innocuously based on the novel amino acid transport systems in eggs and preimplantation conceptuses.